1. Field of the Invention
The invention relates generally to a system of measuring the wavelength of an incoming signal, or spectral discrimination. More particularly, the invention relates to spectral discrimination of optical signals.
2. Description of the Prior Art
An enemy attempting to detect and destroy an aircraft, tank, or ship may transmit an optical signal using a laser or other suitable transmitting device and look for a return signal much like with a radar. To prevent the enemy from receiving an accurate optical return signal, a jamming signal of the same wavelength may be transmitted back. To effectively transmit back a return signal, however, one must quickly and accurately determine the wavelength of the incoming signal transmitted by the enemy.
In the past, determination of the wavelengths of incoming signals, or spectral discrimination, has been performed by using a large number of narrow band filters. A large number of narrowband filters, however, are required so that the wavelength range covered by the narrowband filters can cover the possible wavelength range of every enemy transmitter. In other words, the bandpass region of an individual filter has had to be small so that an incoming signal of a given wavelength can be identified with the wavelength range of a single filter.
To achieve higher resolution, or to detect enemy signals with increasingly narrower wavelength ranges, an even larger number of narrow band (laser line) filters has been required. Wavelength resolution, therefore, has been controlled by the number of filters, and the narrowness of the filter band pass regions.